Frequencies for first 10,000 rows of ab_surf variable in natlterr2014 dataset :

 Surfactant |
      Y Yes |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      1,077       10.77       10.77
          N |      8,762       87.62       98.39
          U |         98        0.98       99.37
          Y |         63        0.63      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 15 Jun 2016